Quantifying a Kiss
by Valerie Vancollie
Summary: Don discovers that Charlie has tried to use math to find the answers to his questions about the encounter. Fourth in the "For Want of a Kiss" series. Don, Charlie


_**Quantifying a Kiss**_

_**by Valerie Vancollie**_

**valeriev84 at hotmail dot com  


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_Characters_: Don, Charlie

_Rating_: PG

_Summary_: Don discovers that Charlie has tried to use math to find the answers to his questions about the encounter.

_Spoilers_: _Identity Crisis_

_Note_: This is the fourth fic in the _For Want of a Kiss_ series. If you haven't read _Siberian Kiss_, _Marked by a Kiss_ and _Kiss & Tell_, you won't be able to follow this fic.

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"Charlie?" Don called out as he entered his childhood home.

When no one responded, Don walked straight through the dining room and stepped into the kitchen, headed for the back door. He knew his father had a class at the moment and since his brother's car was in the driveway that left only one place for him to be if he wasn't in the house. His deduction was proven correct when he found his errant brother in the garage, headphones on and his head bobbing away as his hand raced across the blackboard, equations spilling out of his mind.

Don took a moment to simply watch Charlie before his eyes wandered around the rest of the garage. He sighed and ran a hand through his hair as he caught sight of the equations on the last blackboard. Although the math involved was well over his head, he didn't need to be genius to know what his brother was trying to figure out. Not with his own name in the upper right corner next to an equals sign indicating that the symbol next to it represented him in the algorithm.

He really should have seen this coming. By avoiding all of Charlie's questions and inquiries on the topic, he'd forced his little brother to fall back on the one thing that had almost always allowed him to solve any problem that stood in his way. He wasn't sure what to think of this, though. On the one hand, it annoyed him that Charlie simply couldn't leave the topic alone, couldn't respect his wishes on the matter, but strangely enough, on the other hand, he was also touched. To know that Charlie cared that much that he'd put in the time and effort to try and solve his questions was flattering.

"Hey, Chuck," Don called out loudly, hoping to catch his attention.

Charlie's music, however, was too loud for him to hear the call, so Don angled his approach so his little brother would see him coming. He didn't want to startle him as he'd inadvertently done so often in the past. The problem was, Charlie tended to get so absorbed in his work that he completely lost track of his surroundings and there was no safe way to catch his attention. Well, other than to wait him out, which he really didn't want to do. He'd seen Charlie go at it for hours on end before, not stopping for anything.

"Sorry," Don apologized as Charlie jumped back with a cry as he waved his hand in front of his little brother's face.

"Don! You startled me," Charlie stated, pulling his headphones off and glaring at his brother.

"Hey, I tried to warn you, but you couldn't hear me. You really shouldn't put the music up so loud."

"It helps me concentrate."

"Yeah, whatever," Don replied.

They'd often disagreed on the subject as he couldn't see how the earsplitting noise could possibly be conducive to thinking.

"Did you want something? I'm not done with the expressions for the CalMo case yet."

"Actually, I came by to give you some more data," Don explained, handing over the file he held. "Nikki found some old tax records they kept stored and thought it might help you."

"Yes, that should allow me to narrow things down significantly." Charlie stated as he opened the file and flipped through the pages. "This will be a big help."

"Good," Don responded, stepping past his brother towards the board that had captured his attention earlier. "So, you wanna explain this to me?"

"Huh? What?" Charlie asked, so focused on the data that he'd lost track of his brother's movements, but he flushed as he looked up and saw what Don was pointing at. "Ah, see, well..."

"This is about two Fridays ago, isn't it?"

"You wouldn't tell me anything," Charlie defended, his chin rising stubbornly.

"It was nothing, really."

"I don't think so. He wanted to buy you a beer- he was _flirting_ with you!"

"Yeah, so? It happens."

"I didn't know. You never said anything."

"Why would I? You didn't tell me every time someone flirted with you back then."

"That's different, they were girls."

"That hardly makes a difference," Don countered, raising a finger as Charlie opened his mouth. "And you were in Princeton, we weren't exactly communicating a lot."

"So it happened at college?"

Don sighed and glanced at his watch. Why not? He'd already told Dad, so it was bound to get back to Charlie at some point. Besides, if he refused to answer, his little brother was going to keep digging and sooner or later he might find something. He'd pulled stranger rabbits out of his mathematical hat after all.

"Yes, at a frat party."

"The second?"

"Shortly after I joined the Stockton Rangers, he was one of the relief pitchers."

"The thi-"

"Charlie, no, I am not going to list them all."

"Why not?"

"Because I'm not."

"But I need more data."

"More data," Don repeated in disbelief. "Charlie, what's really fascinating you so much about this?"

"They're guys, men, not women."

"And what does that mean, exactly? 'Cause I know you're not homophobic."

"No! No, I didn't mean it like that. Just... just- I didn't see it coming."

"How could you have? It's not something you could have predicted. You were working off what you knew about me. This has nothing to do with me, well not in that sense anyway. This is all about people that you weren't looking at. It's like..." Don couldn't believe that he was actually searching for a mathematical way to explain the situation, he was spending far too much time around Charlie and his friends. "Having the data on a computer program and then being surprised you didn't see a particular request from a user coming." And had he really just compared himself to a piece of software? "It's an outside influence on the system you were studying."

Apparently Charlie couldn't believe the analogy he'd just made either, if his astonished expression was anything to go by. Well, either that or Don had just made a complete fool of himself by hopelessly botching his analogy. It hadn't sounded _that_ bad, had it?

"You're right, I was neglecting to see it as the result of an external force acting on the dataset I had."

"Yeah, exactly," Don replied, brow furrowing slightly.

"Although, I should perhaps have had an inkling of the possibility," Charlie continued, a very familiar smile appearing on his face and Don's eyes narrowed automatically in response.

He _knew_ that smile. It was the one his little brother always got when he started teasing him about something or other. He was not going to like whatever was coming, that much was guaranteed.

"Do you want to know why?"

"No, not particularly," Don stated, not having the slightest intention of walking into his brother's trap.

"Well, I simply mean, things are rarely completely isolated. There's generally a cause and an effect, or not so much a cause as a factor upon which the external influence acts. To use your analogy," Charlie said with an ironic little gesture in his direction, "the user had a particular reason to make the request they did. It may not have been anticipated by the programmer, but there generally had to be something about the program that caused the user to think their request was compatible with the software. I mean you wouldn't ask Word to do complex calculations after all."

"Depends on the user."

"In your case, though, I think I may know what that factor is," Charlie continued, completely ignoring his comment, the smile only growing as a triumphant expression crossed his face. "Your looks."

"My looks?" Don repeated, scrambling to see where he was going with this.

"Yeah, your prettiness."

The words and teasing tone took a second to penetrate, but when they did, Don's eyes narrowed once more and he lunged forwards. Having expected the response, Charlie tried to dart away, but he underestimated his big brother's speed and Don managed to grab a handful of his outer shirt and prevent his escape. Using the leverage and his superior strength, Don dragged him closer, expertly pinning him against the side of the blackboard with his own body.

"No, Don, be careful of my work!" Charlie protested as he tried to twist himself free without rubbing any of his work off the board.

"Then don't move," Don replied, having been careful to pin him against a blank area, if he moved too much to the left, however...

"Come on, Don!" Charlie whined as Don reached down to the bottom of the board where he normally placed his chalk.

Don completely ignored his little brother as he ran his fingers in the accumulated chalk dust before bringing them up and rubbing them into Charlie's curls despite his vocal protests. When Charlie gave up trying to free himself and ran his own fingers through the chalk dust in order to retaliate, Don grabbed his wrist and tried to bring them to Charlie's own face instead. They struggled for a bit, mock fighting and getting the chalk dust everywhere.

When they finally broke apart, Charlie was proud to see a few streaks of white on his brother's clothes along with one that started in his dark hair and ran passed his ear and onto his right cheek. He knew it was nothing compared to the dust that he was sure he was covered in himself, but at least he'd gotten a few shots in, which was far better than when they'd wrestled as kids.

"You know, it never does work," Charlie finally stated as he gave up trying to wipe the chalk dust off of his layered shirts.

"What?"

"Using expressions and algorithms," Charlie explained with a vague wave at the board that had triggered the whole conversation in the first place. It frustrated him to no end most of the time. Given all of the information he had available on his brother, he should have little trouble making it work, but he couldn't. This current issue was merely another example of that. He'd worked on this for so very long and yet he hadn't seen it coming. There hadn't even been a hint of a clue and it had caught him completely off-guard. "Not when it comes to you."

"Really?" Don questioned with a smile, intrigued and slightly smug.

"Nope. There seem to be too many variables involved, especially ones that are either unpredictable or which I'm simply lacking data on."

"I can live with that," Don stated, throwing an arm over his brother's shoulder, completely ignoring his frustrated frown.

"It's not funny," Charlie said indignantly. "It _should_ work, but it never does."

"That's 'cause I'm doing my job."

"And what's that? Annoying your little brother?"

"Sure, and keeping you on your toes," Don declared as he flexed his arm, pulling Charlie close and messing his hair with his free hand.

"Hey!"

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**Well, this is the last planned fic in this series. I have a very vague idea for another installment, but at this point I simply don't know if it'll develop further into something or not, so just consider this the end and we'll see what happens.  
Also, any feedback on the Don and Charlie interaction here would be much appreciated. I don't write much Charlie and since I'm currently taking part in the Charlie round of _Write-Off_, any feedback would be much appreciated. Thanks!**


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